1. Field of the Invention
The present invention relates to an image pickup device having a collapsible lens unit and a method of controlling the lens unit.
2. Description of the Related Art
Conventionally, a collapsible camera in which a lens barrel is held in the camera body in non-picture-taking mode has widely been used as a compact camera that gives high priority to portability, regardless of whether it is a camera using a silver-salt film (referred to as a silver-salt camera hereinafter) or a digital camera that captures an image as electronic data.
FIGS. 8A and 8B illustrate a collapsible lens unit of a behind-shutter type in which a shutter is located behind a lens system. FIG. 8A shows a relationship in location among an optical lens, a shutter unit and a CCD serving as an image pickup element in picture-taking mode where the lens system is projected. FIG. 8B shows the relationship in collapsed mode where the lens system is collapsed.
An optical lens 11 is made up of one first-group lens 11a, one second-group lens 11b and two third-group lenses 11c arranged in this order from a subject. A shutter unit 12 is provided behind the optical lens system 11.
The shutter unit 12 includes ring-shaped unit base members 12a each having a circular opening. A plurality of semi-circular shutter blades 12b are attached to the unit base members 12a, respectively. The opening/closing of the shutter blades 12b is controlled by an electromagnetic mechanism (not shown). A CCD package 13 is mounted in a given position behind the shutter unit 12 along the picture-taking optical axis AX of the unit 12.
The CCD package 13 includes a CCD 13a serving as an image pickup element. The CCD 13a is fixed on an image-forming plane of the optical lens system 11 with the shutter unit 12 therebetween.
In the collapsed mode shown in FIG. 8B, the first-group to third-group lenses 11a to 11c of the optical lens system 11 are arranged along the picture-taking optical axis AX such that they are close to each other with almost no gap therebetween. The entire lens barrel including the optical lens system 11 can be decreased in length more than that in the picture-taking mode shown in FIG. 8A. Assume here that the optical lens system 11 can be held in the camera body (not shown).
In FIG. 8B, d1 indicates the width of dead space in the direction of the picture-taking optical axis AX. This dead space is a portion in which the lens barrel cannot be collapsed because the shutter unit 12 is fixedly mounted on the CCD package 13.
Jpn. Pat. Appln. KOKAI Publication No. 2003-121720 discloses a lens shutter of not a behind-shutter type but a between-shutter type in which a shutter unit is arranged between lenses. When a lens barrel is collapsed, shutter blades are opened larger and part of the lenses is inserted into the opening of the shutter blades. The lens barrel is thus decreased in length in the optical axis direction, with the result that the device can be thinned when the lens barrel is collapsed.
The lens unit shown in FIGS. 8A and 8B causes the following drawback. Since the shutter unit 12 is fixedly mounted on the CCD package 13 as described above, dead space that does not contribute to the collapse in the direction of the optical axis occurs and the body of the device cannot be thinned.
The between-shutter type lens shutter of the above Publication has to be configured to have such a large opening as to receive part of lenses. Considering that the lens shutter is of a between-shutter type, the lens barrel can be shortened in the optical axis direction when it is collapsed, but it increases in size in the radial direction, with the result that the entire device cannot be downsized.
Since, moreover, the opening of the shutter blades is large, the range in which the shutter blades can be moved extends, and a high shutter speed, which is the feature of the lens shutter, becomes difficult to achieve.